iStock/Thinkstock(NEW YORK) — Days after a historic nuclear accord was struck between six world powers and Iran, then-Republican primary candidate Donald Trump tweeted that the deal posed “a direct national security threat” and called on Republicans to “stand up” and put a stop to it.

Since then, Trump has called it “the stupidest deal of all time,” and his Vice President-elect Mike Pence has vowed the deal would be “ripped up.”

The Iran deal poses a direct national security threat. It must be stopped in Congress. Stand up Republicans!

So, what exactly does the Iran deal guarantee and what could Trump, with backing of a Republican-controlled Congress, do to change it or end it altogether?

The Iran Nuclear Deal

In July 2015, the Obama administration, along with leaders from the U.K., France, Russia, China and Germany (the five permanent U.N. Security Council members plus Germany, known as P5+1), all signed a nuclear accord with Iran that called on Iran to significantly reduce its stockpile of enriched nuclear material and cease further enrichment, effectively extending the time it would take Iran to build a bomb from a few months to a year. The deal also called for a new monitoring system that would allow international inspectors into Iranian nuclear facilities to conduct inspections.

In exchange for the dismantling of some nuclear systems, tens of billions of dollars of frozen Iranian assets were released and major economic sanctions were lifted, allowing foreign companies to conduct business in Iran for the first time in decades. Iran already has new business interests, including deals with U.S.-based Boeing Corp. and the E.U.’s Airbus to buy dozens of passenger jets. Iran is seeing moderate economic growth, but many there feel it’s going slower than promised.

If Iran is found to be in violation of any of the deal’s terms, sanctions could be snapped back into place. The entire agreement is codified in a U.N. Security Council resolution.

A State Department official reiterated to ABC News Monday that the Obama administration believes this deal makes America safer.

“I will say that the Joint Comprehensive Plan of Action (JCPOA) is a very good deal,” this official said. “It effectively cuts off all of Iran’s pathways to a nuclear weapon and ensures the inspections and transparency necessary to verify that Iran is complying and has the full support of the P5+1.”

Renegotiating the Deal

In addition to telling the American Israel Public Affairs Committee (AIPAC) this past May that “my number-one priority is to dismantle the disastrous deal with Iran,” Trump has also suggested that he would “renegotiate” the agreement.

But that would involve convincing all five foreign signatories, plus Iran, to get back to the negotiating table to rework a deal that took years to reach to assuage the views of a newly elected administration in the United States. Most analysts agree that’s not realistic.

Undermining the Deal

Dismantling the deal is very possible, but it’s not simple either.

Trump won’t be able to simply throw is hands up and walk away. He would have to work with Congress to enact measures to undermine it, such as reimposing U.S.-based sanctions that were lifted. He could, for example, recreate the sanctions that prevented U.S. aviation businesses from selling to Iran and in turn scuttle the Boeing deal. That would anger the Iranians and could cause them walk away from the nuclear terms; and it would also likely upset Boeing.

Or he could take a strict enforcement approach to the current plan and attempt to end the deal if Iran falters in the slightest and fails to meet its own obligations. Outside observers opposed to the deal argued last week that Iran has already violated the terms of the deal by exceeding the producing limit of heavy water at its Arak nuclear facility. The U.S. has sought to downplay the incident, saying the Iranians acknowledged the excess and made no attempt to hide it, but a Trump administration could just have easily argued it was a violation.

Any such complaint of a violation would be sent to a “dispute resolution mechanism” as outlined in the agreement, but if that governing body is unable to resolve the issue, the complaining participant would then have the right to end its commitments to the deal.

As State Department spokesman Mark Toner said last week, “the agreement is valid only as long as all parties uphold it.”

Keeping the Deal

The last option — despite Trump’s past statements — is that he leaves the deal alone.

Disrupting the Iran deal could agitate Russia, a country with which Trump has vowed to restore relations. And Trump has praised both Russia and Iran for fighting ISIS, with little regard for the manner in which they, or Syrian President Bashar al-Assad, for that matter, go about doing it.

So, for the sake of a mutual interest in destroying ISIS, he may allow the Iranians to keep the deal. And Trump’s isolationist tendencies might cause him to leave the deal in place, rather than face the prospect of a military operation aimed at dismantling Iran’s nuclear program by force.

In a news conference late Monday, President Obama said that no matter his campaign rhetoric, Trump is going to face the reality that the Iran nuclear deal is working and that it should stay in place.

He said when the deal was be debated the main counterargument was that the Iranians would cheat, but that hasn’t been the case, Obama said.

“To unravel a deal that is working and preventing Iran from pursuing a nuclear weapons would be hard to explain, particularly if the alternative would be to have them freed from any obligations and to go ahead and have them pursue a weapon,” Obama said.

Breaking from the deal would also force the U.S. to start sanctioning China and countries in Europe that have entered into business deals as the agreement allowed.

“When you’re not responsible for it, I think you can call it a terrible deal,” Obama said. “When you are responsible for the deal and preventing Iran from getting a nuclear weapon, you’re more likely to look at the facts.”